Increase max file size and ignore hardlinked duplicates

The first commit increases the maximum file size. Without it, only small files are considered by vmtouch.

The second (larger) commit introduces a new default behaviour that can be deactivated using the new switch -h.

Files that are copies using hardlinks are now not counted only once. As an example:

$ dd if=/dev/random of=first bs=10M count=1
$ cp -al first second
$ vmtouch first second # new behaviour
Files: 1
Directories: 0
Resident Pages: 2560/2560  10M/10M  100%
Elapsed: 0.000571 seconds
$ ./vmtouch -h first second # old behaviour
Files: 2
Directories: 0
Resident Pages: 5120/5120  20M/20M  100%
Elapsed: 0.000803 seconds

As you can see, the old behaviour (with -h) produces output which does not make a lot of sense, as only 10 MByte of real data are cached.

Please review my patches before applying them for good, as my C knowledge is very limited.